In 5- to 6-quart saucepot, heat oil and grated orange peel on medium-high until hot. Add spinach, in 2 to 3 batches, cooking and stirring about 3 minutes or until spinach begins to wilt and it all fits in saucepot. Cover and cook 2 minutes longer, stirring once. Remove saucepot from heat; stir in orange juice and salt. Garnish with orange peel.